The Efficacy, Safety, And Tolerability Of Donepezil HCl (E2020) In Patients With CADASIL Who Have Cognitive Impairment

Inclusion Criteria: * Age range - Adult patients, 25 to 70 years of age inclusive * Gender distribution - Men and women. -- Women of childbearing potential (\<1 year postmenopausal) must be practicing effective contraception and have a negative serum bHCG at Screening. Pregnant and/or lactating females are excluded. Patients who become pregnant during the study will be discontinued. * Diagnostic evidence of CADASIL either by (1) identification of a NOTCH3 mutation (excluding polymorphisms) or (2) presence of typical deposits on an electron microscopy of a skin biopsy. * Cognitive impairment - (1) Subjects or their study partners must give a description of cognitive problems and one of the following: (2a) MMSE score of 10-27 (inclusive) or (2b) Trails B score, 1.5 standard deviations below the mean after adjustment for age and education. * Head MRI - Evidence of disease consistent with CADASIL, and no evidence of another disease, which might account for cognitive impairment or dementia (as judged by the Investigator/physician at the site). (The latter may be determined with a CT head scan for eligibility purposes. The MRI would still be needed.) Must be obtained within 6 months of the Screening/Baseline visit. If no such head MRI had been previously obtained, a head MRI will be obtained as part of Screening/Baseline after all other inclusion and exclusion criteria (except clinical laboratory determinations) are satisfied. Patients in whom an MRI is contraindicated can have a …